Process for preparing esters and products



Patented Nov. 30, 1937 UNITED STATES PRQCESS FOR PREPARING ESTERS ANDPRODUCTS Herman A. Bruson, Elklns Park, Pa., asslgnor to Riihm & HaasCompany, Philadelphia, Pa.

No Drawing. Application December 14, 1934, Serial No. 757,456

16 Claims.

This invention pertains to a process for preparing esters ofalpha-methacrylic acid with primary alcohols, more particularly withprimary alcohols containing more than five carbon atoms.

The already known method for preparing esters of alpha-methacrylic acidsuch as the methyl or ethyl esters, consists in distilling a mixture ofphosphorus pentoxide and the methyl or ethyl ester ofalpha-hydroxy-isobutyric acid. This method, however, when applied to thehigher esters of alpha-hydroxy-isobutyric acid and more particularly tothose esters which contain long fatty chains in the alcohol radical,suchas the lauryl, decyl, cetyl, oleyl or octadecyl esters ofalpha-hydroxy-isobutyric acid, gives products which are of poor qualityfor purposes of polymerization, due to excessive decomposition andcracking induced by the P205 at the, high temperatures necessary fordistilling oif the alphamethacrylates even under high vacuum.Furthermore, during the distillation, a solid mass of meta-phosphoricacid separates which prevents the proper fiow of heat to the stillbottom. This solid mass fuses to the sides of the still and not onlyacts as a catalyst for decomposing the desired product, but alsomechanically coats over the phosphorus pentoxide and renders it unfitfor dehydration. This results in low yields and poor heat economy. Theproducts are always contaminated with decomposition products' which aredeleterious. l

According to the present invention, all of these difliculties areeliminated and high yields of the higher esters of alpha-methacrylicacid obtained, which are of excellent purity by carrying out thedehydration in -an organic volatile liquid which is non-hygroscopic andinert towards phosphoric acid, phosphorus pentoxide and the estersconcerned. The organic liquid should preferably boil below 200 C. atordinary pressure. Suitable liquids are the aliphatic, aromatic, orhydroaromatic preferably saturated hydrocarbons or their chloroderivatives such as benzene, toluene, xylene, solvent naphtha,chlorobenzene, petroleum naphtha, ethylene dichloride, carbontetrachloride, cyclohexane, octane, and the like.

I have found that the quantity of phosphorus pentoxide used alsomaterially affects the purity of the product. An excess of P205 promotesde-' composition whereas if not enough P205 is employed considerableundehydrated hydroxyisobutyric acid ester distils over. For practicalpurposes the quantity of P205 used as an upper limit should not exceedone mol., and as a lower limit should not be less than mol. P305 permol.of

the hydroxyisobutyric acid ester used. It is advantageous to use about0.33 mol. P205 per mol. of hydroxyisobutyrate. The dehydration step iscarried out with agitation at a moderate temperature (-120" C.) untilthe P205 has prac- 5 tically completely dissolved in the mixture of solvent and ester used. Any undissolved particles are then filtered oil andthe clear filtrate distilled to recover the solvent and to fractionatein vacuo the alpha-ethacrylic ester in pure form. Under these conditionsno solid mass separates during the distillation, the still residue beingvery fiuid even at the end of the distillation; thus insuring a highyield of high quality product capable of being readily polymerized.

The following examples aregiven by way of illustrating this process:

Example 1.In a vessel fitted with a stirrer, reflux condenser anddropping funnel, there was placed grams of phosphorus pentoxide and 20200 grams of dry toluene. This suspension was stirred and a solution of150 grams cetyl-alphahydroxyisobutyrate in 100 grams dry toluene,allowed to drip in slowly during the course of about one hour. Noexternal cooling was required, the temperature remaining at (ill- C. Themixture was then stirred for two hours at room temperature (25 C.)during which time'most of the P205 dissolved. The solution was thenwarmed in the course of one hour to 80 C. while stirring. It was thencooled to 25 C. and a small amount of insoluble material filtered ofi.,The clear 111- trate was transferred to a still and the toluenedistilled ofi under ordinary pressure. It is advantageous to add 0.1% ofhydroquinone or alphanaphthol to prevent polymerization of the materialin the still. High vacuum was then applied and thecetyl-alpha-methacrylate boiling within the range 170-212 C./5 mm.collected. The yield was 85% of the theoretical of a product which wascolorless, free from acidity, free from cetene, and of excellentpolymerizing qualities. When heated with 0.2% by weight of benzoylperoxide at 75 C. it polymerizes within 12 hours to a colorless rubberymass, whereas' a sample of cetylalpha-methacrylate made by dry vacuumdistillation of the same amounts of P205 and cetylhydroxyisobutyratedoes not polymerize within '60 hours and often does not polymerize atall, due to the presence therein of acidic and olefinic dcoempositionproducts.

In place of toluene, the same volume of henzene, ethylene dichloride,solvent naphtha or any of the other suitable solvents mentioned hereincan be used.

Emmple 2.One-third mol. equivalent of phosphorus pentoxide was suspendedin about five times its weight of ethylene dichloride, and mixed withone mol. equivalent of lauryl-alphahydroxyisobutyrate dissolved in itsown weight 01' ethylene dichloride. Aiter heating for 1 hour to theboiling point of the solvent, as described in Example 1, the clearsolution obtained was distilled. After the ethylene dichloride came overthe lauryl-alpha-methacrylate distilled as a colorless oilin 85% yield,the main fraction 01' which boiled at 145-165 J5 mm. It polymerlzedreadily when heated at 80 C. with 02% 01' benzoyl peroxide, to acolorless rubbery mass. Benzene or toluene can be substituted for theethylene dichloride.

Example 3.One-halt mol. equivalent of Eros suspended in four times itsweight of benzene was agitated with a 1:1 benzene solution ofstearyl-alpha-hydroxyisobutyrate at 25-30 C. for 3 hours and the mixturefinally heated during 1 hour to 75 C. The. clear solution obtained wasthen distilled. The n -octadecykalphamethacrylate came over in 87% yieldat 190- 210 C./5 mm. It readily polymerizes to a colorlessrubbery masswhen heated 12 hours at 75 C. in the. presence of 0.2% benzoyl peroxide.

In the same manner the following esters were prepared. Theyallpolymerize extremely readily to colorless rubbery masses.

n-hewl-alpha-methacrylate, b. p. C./35 mm., n-octyl-alpha-methacrylate,b. p. 110-120 C./ mm., alpha-ethylhexyl-alphamethacrylate b. p. 136-147"C./'l5 mm. and phen- I ylethyl alpha methacrylate b. p. 100-120 C./2 mm.Y

Bters containing more or less than 5 carbon atoms in the alcoholradical, other than those mentioned can be prepared in accordance withthis invention, the above examples being given merely by way ofillustration and not limitation.

Among these are the heptyl, chloro ethyl andbenayl esters ofalpha-methacrylic acid.

Although I have described the preferred manner of practicing thisinvention, modifications in the procedure can be made without departingfrom its spirit, by using temperatures or proportions diiierent fromthose shown in the examples. Other non-polar solvents which are inerttoward the reacting components can also be used such astetrachlorethane, o-dichlorbenzene, petroleum ether (boiling range90-100 C.), and trichlorethane.

The polymers obtained from the above esters having more than fivecarbonatoms in the alcohol radical are very pure viscous materials andconstitute new compounds which are useful in lubricating oils, laminatedglass, adhesives, rubher compositions, and coating compositions.

I claim:-

1. A process for making esters of alpha-methacrylic acid and primarymonohydric alcohols containing more than five carbon atoms, whichcomprises reacting the corresponding ester of alpha-hydroxyisobutyricacid with from to 1 mol. equivalent of phosphorus pentoxide in thepresence of a volatile organic liquid which is inert towards thereactants; filtering oi! any solid material, and distilling theresulting solution.

2. A process for making esters of alpha-methacrylic acid and primarymonohydric alcohols containing more than five carbon atoms whichcomprises reacting the corresponding ester of alpha-hydroxyisobutyric'acid with phosphorus pentoxide in a solvent which is one of the groupconsisting of volatile, liquid, hydrocarbons and chlorinatedhydrocarbons; removing any insolutained. I

3. A process for making esters of alpha-methacrylic acid and primarymonohydric alcohols containingmore than five carbon atoms whichcomprises reacting the corresponding ester of alpha-hydroxyisobutyricacid with reacting proportions of phosphorus pentoxide in dry toluene;filtering 01! any insoluble matter, and fractionating the clearsolution.

4. A process for making esters of alpha-methacrylic acid and primarymonohydric alcohols containing more than five carbon atoms whichcomprises reacting the corresponding ester of alpha-hydroxyisobutyricacid with reacting proportions or phosphorus pentoxide in dry ethylenedichloride, filteringv ofi any insoluble matter, and

fractionating the clear solution. I

ble matter and distilling the clear solution ob- 1 5. A process formaking lauryl-alpha-methacrylate which comprises reactinglauryl-alphahydroxyisobutyrate and phosphorus pentoxide in va volatileinert organic liquid, filtering of! any insoluble matter, andiractionating the solution obtained.

6. A process for making cetyl-alpha-methaicrylate which comprisesreacting cetyl-alphahydroxyisobutyrate and phosphorus pentoxide in avolatileinert organic liquid, filtering oil. any insoluble matter, andfractionating the solution obtained.

'7. A process for making n-octadecyl-alp amethacrylate which comprisesreacting n-octadecyl-alpha-hydroiwisobutyrate and phosphorus pentoxidein a volatile inert organic liquid, filtering or! any insoluble matter,and i'ractionating the solution obtained.

8. A methacrylic acid ester oi an aliphatic monohydric saturated normalprimary alcohol containing from 8 to 18 carbon atoms in the alcoholradical.

9. Lauryl methacrylate. 10. Stearyl methacrylate. 11. Polymeric laurylmethacrylate. 12. Polymeric stearyl methacrylate. 13. Cetylmethacrylate. 14. Polymeric cetyl methacrylate.

15. A polymeric methacrylic acid ester of an aliphatic monohydricsaturated normal primary alcohol containing from eight to eighteencarbon atoms in the alcohol radical.

16. A process for making esters of a-methacrylic acid and primarymonohydric alcohols containing more than five carbon atoms whichcomprises reacting the corresponding ester' of mhydroxyisobutyric acidwith from one-twelfth to one mol. equivalent of phosphorus pentoxide in.

the presence of a volatile organic solvent which is inert toward thereactants and has a boiling point at atmospheric pressure below 200 C.filtering off any solid material and distilling the resulting solution.

HERMAN A. BRUSON.

